A motion guide device is a mechanical element for guiding linear motion or curvilinear motion of a moving body relative to a base, and is built in various machines such as machine tools, semiconductor/liquid crystal manufacturing apparatuses, auto cars and robots.
FIG. 16 shows an example of such a motion guide device used as one-axis device. The motion guide device has an elongating raceway rail 1 and a moving block 2 mounted linearly and curvilinearly movable thereon. When the raceway rail 1 is mounted on a base 3 and the moving block 2 is a moving body 4 such as a table. Between the raceway rail 1 and the moving block 2, there is a plurality of rolling elements arranged rollably and the moving block 2 slides smoothly along on the raceway rail 1.
In some machines having motion guide devices built therein, the moving body 4 may be displaced slightly in the vertical direction or horizontal direction relative to the base 3 on FIG. 16. For example, for a machine used in adverse environments where wide temperature variations are encountered, if structural elements, such as the base 3 and the moving body 4, have different thermal expansion coefficients, the moving body 4 may be displaced relative to the base 3. Otherwise, if the base 3 is made of aluminum and the raceway rail 1 is made of steel, difference between their thermal expansion coefficients brings about bimetallic action thereby to change a curvature of the raceway rail 1.
When the moving body 4 is displaced in the vertical direction or the horizontal direction relative to the base 3 in a state where the motion guide device is tied between the moving body 4 and the base 3, displacement of the moving body 4 is applied as a load directly to the inside of the moving block. As rolling elements such as balls are arranged between the moving body 4 and the raceway rail 1, if displacement of the moving body 4 is small, such displacement is absorbed by deformation of the rolling elements. However, displacement of the moving body 4 is large, the rolling elements are largely deformed, and such deformation sometimes causes problems of short life duration of the rolling elements and difficulty in smooth rolling of the rolling elements. Hence, if such displacement of the moving body 4 is predictable, a large-size motion guide device is preferably selected, and rollers that can bear a large load are used as the rolling elements.
The applicant has proposed movable-member mounting plates capable of absorbing displacement in the vertical direction or the horizontal direction of the moving body 4 relative to the base 3 (see Patent document 1). As illustrated in FIG. 17, on the upper surface of the moving block, a radial direction plate 5 and a horizontal direction plate 6 are stacked as the movable-member mounting plates. These movable-member mounting plates 5 and 6 have thin portions 5a and 6a, respectively, which are elastically deformed to absorb displacement of the moving body 4 in the vertical direction or the horizontal direction relative to the base 3.    [Patent Document] Japanese Patent Laid-open Publication No. 7-190053